Conventionally, a valuable sheet article such as a paper sheet or a photograph is usually covered with a protective film for protection because such a sheet article is readily suffered from damage. Typically, a sheet laminating apparatus is used for laminating a sheet article between two pieces of protective films. The commercially available sheet laminating apparatuses are usually classified into several types. For illustration, a conventional sheet laminating apparatus is illustrated as follows with reference to FIGS. 1A and 1B.
Referring to FIG. 1A, a schematic cross-sectional view of a conventional sheet laminating apparatus is illustrated. The sheet laminating apparatus 10 of FIG. 1A principally comprises a transfer passage 101, a first roller 102A, a second roller 102B, a first heating unit 103A, a second heating unit 103B and a control unit (not shown). The transfer passage 101 includes an entrance zone 101A, a laminating zone 101B and an exit zone 101C. The first roller 102A and the second roller 102B are respectively disposed on the upper side and the lower side of the laminating zone 101B. When a sandwich structure of a sheet article 12 intervening between a first plastic film 11A and a second plastic film 11B is transported across the laminating zone 101B, the first roller 102A and the second roller 102B presses against opposite sides of the sandwich structure in order to laminate the sandwich structure. During the pressing operation implemented by the first roller 102A and the second roller 102B, the heat energy required to laminate the sandwich structure is offered by the first heating unit 103A and the second heating unit 103B, which are disposed beside the first roller 102A and the second roller 102B, respectively. Generally, the control unit includes a control circuit and a roller driving device for controlling operations of the first roller 102A and the second roller 102B. The roller driving device includes a motor, gear sets and other components for driving the rollers.
Please refer to FIG. 1A again. During operation of the sheet laminating apparatus 10, the first roller 102A is rotated in a first direction R1 and the second roller 102B is rotated in a second direction R2, wherein the first direction R1 is opposed to the second direction R2. As a consequence, a sandwich structure of a sheet article 12 (e.g. a paper sheet) intervening between a first plastic film 11A and a second plastic film 11B is transported through the entrance zone 101A of the transfer passage 101 to the laminating zone 101B. The sandwich structure is laminated in the laminating zone 100B to form a laminate structure, which is then ejected from the exit zone 101C. Meanwhile, the sheet article 12 is fixed between these two pieces of plastic films 12A and 12B.
During the laminating process, the heat generated by the first heating unit 103A and the second heating unit 103B will be transmitted to the first roller 102A and the second roller 102B to soften the first plastic film 11A and a second plastic film 11B and thus the sheet article 12 is fixed between these two pieces of plastic films 12A and 12B. In a case that either the first plastic film 11A is adhered to the first roller 102A or the second plastic film 11B is adhered to the second roller 102B, a so-called jamming phenomenon is resulted. For example, as shown in FIG. 1B, the first plastic film 11A is adhered to the first roller 102A during the laminating process to result in the jamming phenomenon. The conventional sheet laminating apparatus 10 lacks of a jamming-detection mechanism. Generally, the jamming phenomenon is subjectively realized if the laminate structure of the sheet article 12 and the plastic films 11A and 11B has not been ejected from the from the exit zone 101C in a predetermined time period. If the laminate structure is jammed in the transfer passage 101, the user may generally pull out the jammed sheet article by exerting a pulling force on the sheet article. If the problem of getting jammed is very serious, for example the laminate structure of the sheet article 12 and the plastic films 11A and 11B is jammed between the first roller 102A and the first heating unit 103A (or between the second roller 102B and the second heating unit 103B), the pulling force is usually insufficient to pull out the jammed sheet article. Under this circumstance, the sheet laminating apparatus may have an irrecoverable breakdown.
Therefore, there is a need of providing a sheet laminating apparatus having a mechanism for detecting the jamming phenomenon in real time, thereby effectively preventing the sheet laminating apparatus from being damaged by the jammed sheet article.